Blood alcohol content relates directly to the alcohol concentration in alveolar breath. This relationship allows a non-invasive estimation of blood alcohol levels by measuring breath alcohol levels. Simple devices that may be used for field determination of alcohol content in exhaled breath are of increasing interest, not only for police and others charged with regulating highway safety, but for those serving alcoholic beverages, as recent court cases have held such persons responsible for damage done by their intoxicated patrons or guests. A variety of devices for determining alcohol levels of human subjects are known, as for example that shown by Forrester in U.S. Pat. No 2,591,691, which describes a device that permits exhaled breath to be forced through an acidic solution of potassium permanganate at a flow rate of at least 800 ml per minute. By measuring the time required to decolorize the solution, the breath alcohol content, and from that the degree of intoxication, may be estimated. The device is simple and the test is fast, but the color change from pink to colorless is not distinct. The colored oxidizing solution also must be prepared immediately prior to testing, by mixing specific amounts of a standard potassium permanganate solution and a known-concentration sulfuric acid solution, as the solution will deteriorate rapidly on standing.
Permanganate salts coated on solid supports such as molecular sieve, silica gel and clay have been reported by Regen et al., in J. Am. Chem. Soc. 99, pp. 3837-3838 (1977) for oxidation of alcohol in organic solvents at 70.degree. C. under neutral conditions, but not as a colorimetric reagent.
Other devices for semi-quantitative determination of alcohol in breath use the color change produced when ethanol is oxidized by chromate anion under strongly acidic conditions. For example, Grosskopf, in U.S. Pat. No. 2,939,768, discloses a reagent made by impregnating silica gel with potassium dichromate, sulfuric acid, arsenic trioxide and iodine. A simpler version, in which the arsenic trioxide and iodine have been removed, is disclosed by Luckey in U.S. Pat. No. 3,223,488. Other variations have been disclosed. A similar reagent, in which the sulfuric acid has been replaced by metaphosphoric acid, is shown by McConnaughey in U.S. Pat. No. 3,455,654, and the sulfuric acid may be augmented with a pentavalent phosphorous compound and perchloric acid, as shown by McConnaghey in U.S. Pat. No. 3,684,456. Keyes, in U.S. Pat. No. 3,582,274, shows another version which uses a nitric acid solution as the acid source.
Devices based on these reagents have been disclosed as well, as for example the tube of Kral et al., U.S. Pat. No. 3,725,007, which contains glass particles bonded with silica gel that is impregnated with dichromate and sulfuric acid, and the combination of a tube containing acid and dichromate protected by silica-gel desiccant, shown by Gump in U.S. Pat. No. 4,656,008. Rislove discloses, in U.S. Pat. No. 4,791,065, silica gel as a solid carrier for the acid and dichromate.
The color change of the dichromate-acid reagent in the presence of ethanol is relatively distinct and may be from an initial orange or yellow color to an exposed green or dark green color, depending on the manufacturers' methods. The change is slow, however, and the reagents are corrosive and toxic. Chromate is a carcinogen, and both the chromate and the acid are environmental hazards, which complicates disposal.
Thus a need exists for a device and method which permits rapid and reliable estimation of ethanol in breath samples, is safe and easy to manufacture, is stable for storage and easily used in the field, and does not create disposal problems.